Comparing the economics of a heat pump to other heating systems can take a little work since we’re not comparing apples to apples. Different fuels are sold (and priced) in different units: therms or hundred cubic feet (ccf) of natural gas; gallons of propane; gallons of heating oil; tons of pellets; cords of wood; and kilowatt-hours (kWh) of electricity. These different fuels have very different heat values.

Online fuel-cost calculators allow you to plug in the current price of the fuels being compared. The more sophisticated calculators allow you to vary the efficiency with which the fuel is burned (or converted into heat) and even the efficiency with which the heat is distributed, then output a comparison of costs in consistent units—such as dollars per million Btu of delivered heat.

Of course, energy prices fluctuate, so such a comparison is only accurate in the present. But running through these calculations can help you make an informed decision about the costs (and savings) of various heating systems. BuildingGreen’s online calculator (buildinggreen.com/calc/fuel_cost.cfm) was used to create the comparison table below.